From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pekka Enberg Subject: Re: [PATCH 08/40] mm: kmem_cache_objsize Date: Fri, 04 May 2007 21:53:33 +0300 Message-ID: <463B812D.5090009@cs.helsinki.fi> References: <20070504102651.923946304@chello.nl> <20070504103157.215424767@chello.nl> <1178301545.24217.56.camel@twins> <1178302904.2767.6.camel@lappy> <463B7E5C.8030201@cs.helsinki.fi> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, Trond Myklebust , Thomas Graf , David Miller , James Bottomley , Mike Christie , Andrew Morton , Daniel Phillips To: Christoph Lameter Return-path: Received: from courier.cs.helsinki.fi ([128.214.9.1]:54151 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161622AbXEDSxU (ORCPT ); Fri, 4 May 2007 14:53:20 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Christoph Lameter wrote: > SLAB can calculate exactly how many pages are needed. The per > cpu and per node stuff is setup at boot and does not change. We are > talking about the worst case scenario here. True in case of an off slab > we have additional overhead that would also have to go into worst case > scenario. Fair enough. But there's no way it can take into account any slab management structures it needs to allocate. The slab simply doesn't know how many pages are needed to _allocate n amount of objects_. Peter is interested in a _rough estimate_ so I don't see the point of adding that kind of logic in the slab. It's an API that simply cannot satisfy all its callers which is why I suggested exposing buffer size in the first place (the slab certainly knows how many bytes it needs for one object). Pekka